Chapter 22: Vestibular system Flashcards
vestibular system
-functions to keep us visually and physically steady in the world
- Contributes to maintenance of balance and equilibrium:
- head movement and position relative to gravity
- Gaze stabilization- VOR
- Postural adjustments
- Autonomic function and consciousness (connections to reticular formation, problems indicate problem in homeostasis)
*Vestibulospinal tracts- keep us upright- Brainstem so we have a low degree of direct voluntary control
Cerebrocortex=conscious cortex
Vestibular apparatus
Inner ear-just inside, buried deep
CN VIII- Cochlea (hearing part), Vestibular part (balance part)
Considering vestibular- balance part in this chapter
Semicircular canals
5 pieces
-between all there they detect any movement
-3 per side
-anterior- 45 degrees off centered pointing in front
-posterior- 45 degrees off centered behind
Horizontal- lateral a bit tilted
hair cells in fluid
seaweed and shamrocks (seaweed is hair follicles)
-At end of canals there is ampula- in ampula there are hair cells- when straight up they are still sending some action potential to tell there is no movement.
When head moves- hair cells send more action potential
-Bent to the opposite side- hair cells send less action potential
Baseline activity** hair cells always sending signals
Semicircular canals detection
detects angular movements of head
- really sensitive to being bent and unbent (acceleration and deceleration)
- the side you turn to sends more action potential
- the side you are turning away from sends less action potential
semicircular canals paired activity
takes pairing to let brain know which way you are moving
- R anterior and L posterior detect movement in one plane
- L anterior and R posterior detect movement in one plane
- R and L horizontal detect movement in one plane
Review
Optokinetic reflex and optokinetic nystagmus are the same thing
-optokinetic reflex works both with slow head moving, object not (this does not excite inner ear because it is a slow movement object moving, head not)
-Nystagmus is a fast reset to find another object (something new) to track (driving down the street)
Review
Right optic tract damage produces left homonymous hemianopsia
peripheral vestibular system
detects angular movement
Otolithic organs
include:
- Utricle
- Saccule
- Linear movements and pull of gravity
- Utricle- horizontal
- Saccule- linear/verticle
Otoconia- blobs on top of hair cells
Otolithic organs
- Haircells are in jelly
- baseline activity
- Depolarization
- -gravity, linear, acceleration, deceleration
vestibular nerve
From vestibular apparatus to brainstem nuclei
- Pathway from CN VIII-vestibular system
- Ends at belt line- pons and medullar junction
Central vestibular system-vision
part of equilibrium, helps vestibular nuclei know how we are positioned
Central vestibular system-Proprioception
connected to muscle spindles
Central vestibular system-Weight shifts
Gets information from superficial sensors like pressure and touch
Central vestibular system- Auditory information
Sound can help confirm movement for vestibular nuclei
-vestibular nuclei receives all information- conceives it, decides what needs to be done to stay upright
central vestibular system
There is a pathway that goes to cerebral cortex so you know equilibrium and confirm it
eye movement
Vestibular system outputs to eyes to VOR to help visual work keep steady
MLF- Medial longitudinal fasciculus
vestibular nuclei excite to the MLF to keep vision steady and keeps eyes moving together
-Superior colliculus responds to visual input
Head movement
Vestibular nuclei- Sends signals to muscles that control head- stay up in pull of gravity
-Vestibular nuclei- directly control head movement
Posture of head and body
Medial and lateral vestibulospinal facilitated to catch on side of fall and inhibit on opposite side to get back upright
Reticular formation
- Sometimes movement of head and body change homeostasis
- If reticular formation determines movement is threat to homeostasis- get nauseous- still threat- throw up
Visual-Vestibular interaction
Activity in the visual cortex and vestibular are reciprocally inhibitory:
- Increased visual cortex activity inhibits the vestibular cortex
- Increased vestibular cortex activity inhibits the visual cortex
*reciprocally inhibitory (a lot of visual stimulation-vestibular becomes inhibited)
Signs and Symptoms of vestibular disorders
damage to peripheral receptors (semicircular canals and otolithic organs) or to CN, Brainstem nuclei, central projection axons, or cortical reception areas.
Pusher syndrome- pathway from inner ear to cortex gets damaged- Pt feels like they are falling over and when they try to push themselves back to alignment they are actually pushing self over.
S&S
- vertigo
- nausea/vomiting
- Pathologic nystagmus
- Disequilibrium (impaired gaze stabilization)
- Vestibular ataxia (don’t feel upright or mvmt)
- Oscillopsia (complete lack of gaze stabilization, complete lack of VOR)
Need to distinguish
distinguish:
- peripheral (BPPV) vs. central
- Unilateral vs. Bilateral
- Hyperfunction vs. Hypofunction
normal peripheral vestibular function
at rest= size of the two signals tells you the amount of action potential being sent
-Head turn to the right
AP goes up on right side
AP goes down on left side
eyes see, body feels, inner ear system messages confirmed
Unilateral hyperfunction (peripheral BPPV)
vestibular apparatus malfunctioning and one side is more active than it should be
-Benign paroxysmal positional vertigo (BPPV)- not deadly, no apparent cause, occurs with certain positions/movements of head, spinning)
Posterior- turn head 45 degrees, tilt back
-Nystagmus quick phase is in direction of way head is moving- in direction of pathology
- acute comes on all at once mismatch- out of all of the possible symptoms two show up the most:
- PROFOUND DIZZINESS (due to mismatch)
- NAUSEA- due to acute mismatch, especially vertigo
definition- Crystals floating in semicircular canal
cause inappropriate excitation.
This causes one inner ear to effectively
signal “I’m moving” even when the head
is still.
hyperfunction (BPPV) unilateral peripheral
- dizziness
- Nausea
- Postural instability- conditions present but usually individual stays put (person doesn’t want to move)
- Reduced gaze stabilization- VOR temporarily broken, person does not move so not very present
Unilateral hypofunction (peripheral, neuritis)
-vestibular neuritis- squeezing of CN VIII- one side has too little signal- night night
- Neuritis- compression of CN VIII where pierces the skull to go into the brainstem- does not come on as big or as acutely (it sneeks up on you, and is a little bit more insidious onset)
- input from one ear insidiously drops/goes away
Damage to Cranial Nerve VIII on one side leads to reduction of action potentials from one inner ear. This results in a chronic mismatch of signals from the two ears.
- Right ear isn’t available to tell me that the head is turning to the right (world is blurry because my eyes go with my head and I have to focus on the world as I move, Like running with camera on cops (no gaze stabilization)
- Less signals from the right inner ear means that in the vestibulospinal tracts, the right side wont be as facilitated as the left and so they will have less postural stability on one side because of the difference in input
- blurry when I turn head, when I walk, and I feel unstable
S&S of neuritis
(hypofunction/peripheral/ unilateral)
- reduced gaze stabilization, especially to one side
- postural instability (impaired VOR and reduced vestibulospinal activity)
- Dizziness
- Nausea
- doesn’t report vertigo because there is no acute mismatch, doesn’t report nausea because there is no acute mismatch
- very likely will report feeling dizzy but not spinning, just unstable.
- body cant accommodate to the loss of OR and loss of vestibulospinal tract (have to become good at consciously controlling the eyes). make the VOR reflex a conscious stabilization of the world=TREATMENT (gaze instability and blurriness)
Hypofunction (bilateral peripheral)
- -significantly reduced gaze stabilization:
- Oscillopsia- no visual stability with head movements (like cops camera)
Kills sensors of the ears on both sides (no VOR at all)
-will have postural instability because the vestibulospinal tracts have been lost or less facilitated on both sides
Some drugs can have a way of destroying neurons in CN VIII (ototoxic)
